Optical recording medium and disc cartridge having 2 GB capacity

ABSTRACT

An optical recording medium is provided which has a substrate and a signal recording layer provided on the substrate and in which an information signal is recorded in the form of microscopic pits. A light beam is focused on the signal recording layer and some change of the light beam carried by a return light from the signal recording layer is detected to read the information signal recorded on the signal recording layer. The optical recording medium has a diameter of 65 mm or less and thickness of 0.4 to 0.7 mm. An information signal recording area extends outwardly from a radial position of 12.5 mm or less from the center of the medium. The ratio in area between the information signal recording area and non-signal recording area is 3.4 or more. The storage capacity of this medium is 2 gigabytes or more. The optical recording medium has formed at the center thereof a center hole around which an annular table-abutment convexing to one side of the medium is formed. A magnetic-clamping hub is installed in the center hole and thus the medium is magnetically clamped to a rotation driving mechanism of an optical recording and/or reproducing apparatus. The compactness and high density of recording of the optical recording medium will contribute greatly to a further compact structure of a recording and/or reproducing apparatus in which the medium is to be used.

RELATED APPLICATION DATA

This application is a divisional of application Ser. No. 09/399,255,filed Sep. 20, 1999, abandoned. The present and foregoing applicationsclaim priority to Japanese Application No. P11-176029, filed on Jun. 22,1999. All of the foregoing applications are incorporated herein byreference to the extent permitted by law.

BACKGROUND OF THE INVENTION

The present invention relates to an optical recording medium including asubstrate and a signal recording layer provided on the substrate and inwhich an information signal recorded on the signal recording layer isreproduced optically or by detecting a change of the reflected lightfocused onto the signal recording layer, and to a disc cartridgeencasing the optical recording medium.

As one of the conventional recording media for audio and videoinformation, optical discs, from which recorded information is readusing a light beam or to which information is written using a lightbeam, are widely used. Since such an optical disc is formed from asingle plate-like substrate, it can easily be handled and has a largerstorage capacity than other recording media such as magnetic tapes, etc.Therefore, the optical discs are widely used as media for recordingaudio and video information, computer-processed data, etc.

Information processing units, such as computers, have been designed moreand more compact with an increasingly smaller internal space ofinstallation for a recording and/or reproducing apparatus using anoptical recording medium such as an optical disc or the like. That is,there is a demand for a smaller design of such a recordingand/reproducing apparatus.

There are various types of portable or carry-on recording and/orreproducing apparatuses for recording and/or reproduction of audio andvideo information. For a higher portability, it is also demanded thatthe apparatuses be of a more compact design.

For such a smaller recording and/or reproducing apparatus, a recordingmedium used in the apparatus should be correspondingly smaller whilehaving a larger storage capacity.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a noveloptical recording medium designed smaller while having a larger storagecapacity, and a disc cartridge in which the optical recording medium isencased.

It is another object of the present invention to provide an opticalrecording medium having a larger storage capacity while contributing toa more compact design of a recording and/or reproducing apparatus inwhich the optical recording medium is used, and a disc cartridgeencasing the optical recording medium.

It is a further object of the present invention to provide an opticalrecording medium designed smaller and positively mountable on a rotationdriving mechanism to be rotatable along with the rotation drivingmechanism, and a disc cartridge encasing the optical recording medium.

In an embodiment, an optical recording medium according to the presentinvention includes a substrate and a signal recording layer provided onthe substrate, an information signal being recorded on the signalrecording layer. The optical recording medium has a diameter of 65 mm orless and a thickness of 0.4 to 0.7 mm. An information signal recordingarea extends outwardly from a radial position of 12.5 mm or less fromthe center of the medium. A ratio between the information signalrecording area and a non-recording area is 3.4 or more. A storagecapacity is at least 2 GB (gigabytes) or more.

The above optical recording medium has formed at the center thereof acenter hole around which there is formed an annular table-abutment beingconvex to one side of the medium and in which a hub or clamping plate isfixed.

In an embodiment, an optical recording medium according to the presentinvention includes a substrate and a signal recording layer provided onthe substrate, wherein an information signal recorded on the signalrecording layer is reproduced by detecting a change of the reflectedlight focused onto the signal recording layer. The optical recordingmedium has a diameter of over 38 mm and under 52 mm and a thickness of0.4 to 0.7 mm. An information signal recording area extends outwardlyfrom a radial position of 12.5 mm or less from the center of the medium.A storage capacity is at least 1 GB or more.

The above optical recording medium has formed at the center thereof acenter hole around which there is formed an annular table-abutment beingconvex to one side of the medium and in which a hub or clamping plate isfixed.

In an embodiment, an optical recording medium according to the presentinvention has an annular table-abutment for placement on a disc table ofa rotation driving mechanism, and a hub which is to be attracted by amagnet disposed on the disc table, whereby the medium can be rotatedalong with the disc table.

In an embodiment, an optical recording medium according to the presentinvention is a read-only optical recording medium. It includes asubstrate, formed to a thickness of 0.4 to 0.6 mm by injecting resinwithin a mold prepared by stamping a stamper having formed thereon a pitpattern in which the recording track pitch and smallest-pit length areabout 1.4 times larger than those in a first optical recording mediumwith a storage capacity of at least 2 GB including a substrate, and asignal recording layer provided on the substrate, and in whichinformation signal recorded on the signal recording layer is reproducedby detecting a change of the reflected light focused onto the signalrecording layer; and a light-transparent sheet which is 0.05 to 0.1 mmin thickness and having on one side thereof a pit pattern, formed bythermally stamping a pit-pattern stamper, where a signal recording layeris formed. In the optical recording medium, the substrate and sheet arejoined to each other with their respective pit-pattern sides placed in aface-to-face relation through a light-transparent layer of 20 to 35 μm.The first optical recording medium having a diameter of 65 mm or lessand a thickness of 0.4 to 0.7 mm, an information signal recording areadefined thereon extending outwardly from a radial position of 12.5 mm orless from the center of the medium, a ratio in diametrical length of 3.4or more between the information signal recording area and anon-recording area, and a storage capacity of at least 2 GB. It has adiameter of 65 mm or less and a thickness of 0.4 to 0.7 mm. Aninformation signal-recorded area defined thereon extends outwardly froma radial position of 12.5 mm or less from the center of the medium. Astorage capacity is a half or less of that of the first optical discrecording medium.

In an embodiment, the optical recording medium is a read-only type. Ithas a diameter of over 38 mm and under 52 mm and a thickness of 0.4 to0.7 mm. An information signal recording area extends outwardly from aradial position of 12.5 mm or less from the center of the medium.

In an embodiment, a disc cartridge according to the present inventioncomprise an optical disc including a substrate; a signal recording layerprovided on the substrate and in which an information signal recorded onthe signal recording layer is reproduced by detecting a change of thereflected light focused onto the signal recording layer, the opticaldisc having a diameter of 65 mm or less and a thickness of 0.4 to 0.7mm, an information signal recording area defined thereon extendingoutwardly from a radial position of 12.5 mm or less from the center ofthe optical disc, a ratio of 3.4 or more between the information signalrecording area and a non-signal recording area, and a storage capacityof at least 2 GB or more; and a rectangular cartridge in which theoptical disc is encased. In the disc cartridge, a writing and/or readingaccess opening is formed in a side thereof to which an optical pickup tofocus a light beam on at least the optical disc is opposite throughwhich a radially extending portion of the optical disc is exposed, and acentral opening is also formed through which a center hole formed at thecenter of the optical disc is exposed. The writing and/or reading accessopening is formed deviated to one lateral side from the middle point ofthe front side of the cartridge.

In an embodiment, a disc cartridge according to the present inventionencases an optical disc including a substrate and a signal recordinglayer provided on the substrate, and in which an information signalrecorded on the signal recording layer is reproduced by detecting achange of the reflected light focused onto the signal recording layer.In an embodiment, a disc cartridge has a diameter of over 38 mm andunder 52 mm and a thickness of 0.4 to 0.7 mm. An information signalrecording area extends outwardly from a radial position of 12.5 mm orless from the center of the medium. Its storage capacity is at least 1GB.

A disc cartridge according to the present invention encasing theabove-mentioned read-only optical disc has a reading access openingformed only in a lower half.

These objects and other objects, features and advantages of the presentintention will become more apparent from the following detaileddescription of the preferred embodiments of the present invention whentaken in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first optical disc according to thepresent invention, showing the upper side thereof.

FIG. 2 is a perspective view of the optical disc in FIG. 1, showing therear side thereof.

FIG. 3 is a sectional view of the optical disc in FIG. 1.

FIG. 4 is a sectional view of the optical disc in FIG. 1, set on therotation driving mechanism of a disc recording and/or reproducingapparatus.

FIG. 5 is a sectional view of the optical disc in FIG. 1, showing thesignal recording layer.

FIG. 6 schematically illustrates reading of information signal recordedon the optical disc in FIG. 1.

FIG. 7 is a sectional view of a second optical disc according to thepresent invention.

FIG. 8 is a sectional view, enlarged in scale, of a third optical discaccording to the present invention, this optical disc being of aread-only type.

FIG. 9 schematically illustrates the process of manufacturing a sheetfrom which the read-only optical disc is produced.

FIG. 10 is a sectional view of the read-only optical disc, showing howthe substrate and sheet thereof are joined together.

FIG. 11 is a sectional view of An embodiment of the read-only opticaldisc according to the present invention.

FIG. 12 is a perspective view of a first disc cartridge in which thefirst optical disc is encased.

FIG. 13 is a perspective view of the first disc cartridge, showing therear side thereof.

FIG. 14 is a perspective view of a second disc cartridge encasing thesecond optical disc.

FIG. 15 is a perspective view of the second disc cartridge, showing therear side thereof.

FIG. 16 is a plan view of an adapter used to allow the second disccartridge to have same dimensions as the first disc cartridge.

FIG. 17 is a sectional view of the adapter in FIG. 16.

FIG. 18 is a plan view of the second disc cartridge set in the adapter.

FIG. 19 is a perspective view of an optical recording and/or reproducingapparatus in which the optical disc according to the present inventionis used.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Referring to FIGS. 1, 2 and 3, there is schematically illustrated afirst optical disc according to the present invention. The optical discis generally indicated with a reference 1. As shown, the optical disc 1includes a substrate 2 made of glass or a light-transparent syntheticresin such as polycarbonate resin to be 65 mm or less in diameter and0.4 to 0.7 mm in thickness, and having a signal recording layer formedon one side thereof.

More specifically, the optical disc 1 consists of the substrate 2 madeof polycarbonate resin to have a diameter R₁, of 64 mm and a thicknessD₁ of 0.6 mm as shown in FIG. 3. The substrate 2 has formed therein atthe center thereof a center hole 3 having a diameter R₂ of 8 mm. Thesubstrate 2 has formed around the center hole 3 an annulartable-abutment 4 being convex to one side of the substrate 2. Thetable-abutment 4 is to be placed on a disc table of a rotation drivingmechanism in an optical recording and/or reproducing apparatus in whichthe optical disc 1 is set. The table-abutment 4 has an outside diameterR₃ of 14 mm, and is convex approximately D₂ equal to the thickness D₁ ofthe substrate 2 from one side of the latter.

There is provided at the center of the substrate 2 a magnetic clampinghub 5 to close the center hole 3. The hub 5 is formed from a thin plateof a magnetic metal such as iron. As shown in FIG. 3, the hub 5 consistsof a depressed portion 6 formed at the center thereof for fitting intothe center hole 3, and a flange portion 7 formed around the depressedportion 6 for fixing to the substrate 2. The depressed portion 6 thushas the form of a bottomed cylinder. The depressed portion 6 has formedtherein at the center thereof a spindle hole 8 in which a spindle of therotation driving mechanism engages. The spindle hole 8 has a diameter R₄of 2.0 mm. The table-abutment 4 is concaved as indicated with areference 9 in its convexing direction.

As shown in FIG. 3, the hub 5 is secured to the substrate 2 with thedepressed portion 6 thereof fitted in the center hole 3 of the substrate2 and the flange portion 7 engaged in the concavity 9 of the substrate2. The hub 5 is fixed at the flange portion 7 thereof in the concavity 9with an adhesive. Also as seen from FIG. 3, the hub 5 is fixed to thesubstrate 2 so that a lower surface 6 a of the depressed portion 6positioned at the side of the table-abutment 4 will not protrude from alower surface 4 a of the table-abutment 4. That is, the height of thehub 5 from the lower surface 6 a of the depressed portion 6 to theflange portion 7 is designed smaller than the thickness of thetable-abutment 4 of the substrate 2.

As described above, the optical disc 1 includes the substrate 2 providedwith the table-abutment 4 and hub 5 is set on a rotation drivingmechanism 11 of an optical recording and/or reproducing apparatus asshown in FIG. 4. The rotation driving mechanism 11 consists of a spindlemotor 12, a spindle 13 driven by the motor 12, and a disc table 14 fixedat an end of the spindle 13 rotatably with the spindle 13. The disctable 14 has a disc-abutment 15 formed along an outer circumferencethereof and a concavity 16 formed inside the disc-abutment 15 and inwhich an annular magnet 17 is fixed. The magnet 17 is secured to beflush with an upper surface 15 a of the disc-abutment 15 or not toprotrude from the disc-abutment surface 15 a. The optical disc 1 is seton the disc table 14 by placing the table-abutment 4 on thedisc-abutment 15 with the spindle 13 fitted into the spindle hole 8 ofthe hub 5. The hub 5 of the optical disc 1 is attracted by the magnet 17and is thus securely held on the disc table 14. Thus the optical disc 1can be rotated along with the disc table 14.

The spindle 13 is formed to have generally a same diameter as thespindle hole 8 so that the center of rotation of the optical disc 1 cancoincide with the axis of the spindle shaft 13 for correct setting ofthe optical disc 1 on the disc table 14.

As aforementioned with reference to FIG. 3, the hub 5 is fixed to thesubstrate 2 so that a lower surface 6 a of the depressed portion 6positioned at the side of the table-abutment 4 will not protrude fromthe lower surface 4 a of the table-abutment 4. Therefore, when theoptical disc 1 is set on the disc table 14, it will be in the vicinityof, but not in contact with, the magnet 17. Since the hub 5 is placed inthe vicinity of the magnet 17, the optical disc 1 is attracted towardthe disc table 14 by a large magnetic attractive force and thus can berotated along with the disc table 14. When the optical disc 1 is set onthe disc table 14, the hub 5 will not be in contact with the magnet 17,so that no excessive attractive force will act on the hub 5 and hencethe optical disc 1 can easily be set onto or removed from the disc table14.

Since the hub 5 is secured to the substrate 2, for the depressed portion6 thereof to be positioned at the side of the table-abutment 4, thespindle 13 can be engaged in the spindle hole 8 of the hub 5 to asufficient amount even if its protrusion from the disc table 14 issmall. For example, if the spindle 13 is provided with a taper centeringend portion 8 a as shown in FIG. 4, it can be formed to such a heightthat it will not protrude from the optical disc 1 and can center thelatter. By forming the spindle 13 to a limited length or height, therotation driving mechanism 11 can be designed to have a limited heightand hence a recording and/or reproducing apparatus using the lowrotation driving mechanism 11 can be designed thinner.

The magnet used in the conventional magnetically clamping rotationdriving mechanism has a strength BHmax of about 30 MG oersteds. In thisembodiment, the optical disc 1 includes the substrate 2 made ofpolycarbonate resin to have the diameter R₁ of 64 mm and thickness D₁ of0.6 mm. To keep the optical disc 1 magnetically clamped to the disctable 14 from easily being separated from the disc table 14 even whenthe latter is applied with a shock, a magnetic attractive force of 120 gor so is required. With such an attraction, the optical disc 1 can berotated together with the disc table 14 even at a rotating speed of4,000 rpm or more.

To obtain such a magnetic attractive force using the magnet used in theconventional rotation driving mechanism, the hub 5 should have a surfaceof 8 mm or so in diameter to be attracted by the magnet. Also, to holdthe optical disc 1 having the diameter R₁ of 64 mm horizontally on thedisc table 14, the annular table-abutment surface 4 a around the hub 5should be 2.6 mm or so wide. However, it is difficult for the reason ofmolding technique to form the table-abutment 4 convex to one side of thesubstrate 2 and having a high flatness over its whole lower surface 4 ato every corners. More specifically, a range of 0.2 mm or so on eitherend of the table-abutment 4 cannot be counted as the table-abutmentsurface 4 a. Taking these factors in consideration, the table-abutment 4should be formed to a diameter of at least 14 mm or so in case the hub 5of 8 mm or so in diameter, which is to be attracted by the magnet 17, isdisposed at the center of the table-abutment 4 and inside the lower ortable-abutment surface 4 a of 2.6 mm or so in diameter.

As having been described above, the optical disc 1 has formed at thecenter thereof the table-abutment 4 convex to one side of the substrate2 and in which the hub 5 is to be fixed. Further the optical disc 1 hasa signal recording layer 21 formed on the other side of the substrate 2as shown in FIG. 5, for example. The signal recording layer 21 consistsof a recording layer 22, auxiliary recording layer 23, non-magneticlayer 24 and perpendicular magnetic layer 25 stacked in this order onthe substrate 2.

The recording layer 22 is formed from a film of a material, such asGdFeCo alloy, having a magnetic axis parallel to the layer surface atroom temperature and which will be magnetized in a directionperpendicular to the layer surface at a temperature approximate to areading temperature attained when heated with a light beam focusedthereon for reading an information signal recorded on the optical disc1. The auxiliary recording layer 23 is provided to improve the readingresolution and thus the reading characteristic and is formed from a filmof a material, such as GdFe alloy, having a Curie temperatureapproximate to the reading temperature attained when heated with thereading light beam, having a magnetic axis parallel to the layer surfacebefore it is heated up to the Curie temperature, and losing the magneticaxis parallel to the layer surface after it is heated up to a highertemperature than the Curie temperature. More particularly, at a lowertemperature than the Curie temperature, the recording layer 22 has aswitched connection with the auxiliary recording layer 23 and thus hasan intra-plane magnetized status in which the direction of magnetizationis parallel to the layer surface. On the other hand, at a temperaturehigher than the Curie temperature, the auxiliary recording layer 23loses the direction of magnetization and thus the recording layer 22 hasa magnetostatic connection with the perpendicular magnetic layer 25 andis perpendicularly magnetized in the magnetized direction of therecording magnetic layer 25.

The non-magnetic layer 24 is provided to reduce the influence of therecording layer 22 on the recording magnetic layer 25 when aninformation signal is written to the recording magnetic layer 25. It isformed from an AlN or SiN film, for example.

The recording magnetic layer 25 is an amorphous ferromagnetic layer ofwhich the magnetic easy axis is perpendicular to the layer surface. Itis formed from a film of an amorphous ferromagnetic material having alarge coercive force at room temperature and a Curie point approximateto 200° C., such as a TbFeCo alloy or a TbFeCo alloy to which an elementof the fourth group such as Cr is added in a very small amount.

The signal recording layer 21 constructed as described above has areflective metal layer 26 formed thereon. The reflective metal layer 26is made of a high reflectivity, nonmagnetic metal to reflect 70% or moreof the light beam incident upon the optical disc 1. This material shouldpreferably be a good thermal conductor such as Al, Au, Ag or the like.The reflective metal layer 26 is protected by a protective layer 27 of aphoto-curing resin or the like formed on the reflective metal layer 26.

To write an information signal to the signal recording layer 21 of theoptical disc 1 constructed as above-mentioned, pulse-irradiated magneticmodulation is used in which a light beam is pulsed for each recordingdata clock to modulate the recording magnetic field according to therecording data. This technology enables a higher density of recordingthan the conventionally used light intensity modulation. Morespecifically, with the pulse-irradiated magnetic modulation, pits havinga same shape as a beam spot focused by an objective lens on the signalrecording layer 21 are written to overlap one on the other on therecording magnetic layer 25, whereby an information signal can berecorded beyond an optical limit depending upon a light spotdistribution (λ/NA) determined from a relation between a wavelength λ ofa light beam generated in the light intensity modulation and a numericalaperture NA of the objective lens by which the light beam is focusedonto the signal recording layer.

To write an information signal using pulse-irradiated magneticmodulation, a light beam of 380 to 420 nm or 630 to 670 nm in wavelengthλ is used. An objective lens having a numerical aperture NA of 0.5 to0.7 is used to focus the light beam onto the signal recording layer.Recording tracks with a pitch of 0.3 to 0.55 μm are formed to write theinformation signal along them and with a pit length of 0.1 to 0.22μm/bit.

When the numerical aperture NA of the objective lens is 0.6 and theworking distance between the objective lens and optical disc 1 is 1.1mm, a light beam emitted from a semiconductive laser and formed to be aparallel light incident upon the objective lens has a diameter of 3 mm.In this case, the objective lens upon which the parallel light of 3 mmin diameter is incident should have a diameter of 4 mm. Thus, a lensbobbin supporting the objective lens has to be 5 mm or more in diameter.To control the focusing and tracking of the laser beam outgoing from theobjective lens supported by the lens bobbin and which scans the signalrecording area of the optical disc 1, the lens bobbin is installed on abiaxial actuator which drives to move the objective lens in a focusingdirection parallel to the optical axis of the objective lens and in atracking direction perpendicular to the optical axis. Therefore, a spaceof about 1.5 mm for part installation has to be provided outside thelens bobbin.

The optical disc 1 has the table-attachment 4 of 14 mm or so in diameterprovided at the center thereof. The recording and/or reproducingapparatus has disposed therein the disc table 14 having generally thesame size as the table-attachment 4 and on which the table-attachment 4is to be mounted. When the optical disc 1 constructed as mentioned aboveis scanned with a light beam emitted from an optical pickup unit usingthe objective lens of 4 mm in diameter, the center of the light beam canbe moved to a radial position of 11 mm near the lead-in area of theoptical disc 1. That is, the light beam cannot be irradiated to an innerarea having a diameter R₅ of 22 mm. Therefore, the optical disc 1 has aninformation signal recording area defined outside the inner area havingthe diameter R₅ of 22 mm.

To assure accurate optical read, by a light beam, of an informationsignal recorded as magneto-optical signal in the information signalrecording area, a birefringence by the substrate 2 has to be 30 nm orless for reciprocation of the light beam. Therefore, the informationsignal recording area is defined outside the inner area having thediameter R₅ of 22 mm and in which the birefringence of light beamindicated upon the substrate 2 is assured to be less than 30 nm forreciprocation.

As shown in FIG. 3, the optical disc 1 has a signal recording areaextending outwardly from a radial position of 12.5 mm or less from thecenter of the optical disc 1, namely, from a diametrical position R₆ of25 mm or less, to positively write a maximum amount of an informationsignal to the optical disc 1 and also to positively read a recordedinformation signal from the optical disc 1.

More specifically, the optical disc 1 has defined thereon an audio andvideo information signal recording area of which the inside diameter R₆is 24.5 mm and the outside diameter R₇ is 61 mm. Further, on the opticaldisc 1 are formed, inside the signal recording area, an area in whichcontrol signals, etc., which are used for information signal write toand read from the optical disc 1, are recorded, and, outside the signalrecording area an area in which control signals, etc., which areindicative of the end of the signal recording area, are recorded.

In the optical disc 1 constructed as in the above, the ratio between theinformation signal recording area and non-information signal recordingareas is 3.4 or more.

If pulse-irradiated magnetic modulation is adopted with the optical disc1 according to the present invention, use of a light beam of 400 nm inwavelength λ permits to recording of record 4 gigabytes or more of aninformation signal, while use of a light beam of 660 nm in wavelength λpermits to recording of 2 gigabytes or more of an information signal.

Since it is possible to record 2 gigabytes or more of an informationsignal on the optical disc 1, conventionally proposed signal compressiontechnology can be used to record many pictures. For example, the JPEGstandard can be used to record 200 or more still pictures, and the audiocoding technique included in the MPEG2 standard can be used to record anMPEG2 moving picture (transfer rate of 8 Mbps) for more than 30 minalong with sound.

To read an information signal recorded on the optical disc 1 usingpulse-irradiated magnetic modulation as described above, a light beam L₁is irradiated to the optical disc 1 through the substrate 2 as shown inFIG. 6. When the light beam L₁ is irradiated to the optical disc 1, aportion of a recording layer 22 formed from a GdFeCo alloy film on whichthe light beam L₁ is focused is heated to a higher temperature thanpredetermined. A portion of the auxiliary recording layer 23 formed fromthe GdFe alloy film on which the light beam L₁ is focused is heated to ahigher temperature than the Curie temperature and loses the direction ofmagnetization. As a result, the heated portion of the recording layer 22has a magnetostatic connection with the recording magnetic layer 25 andis perpendicularly magnetized in the magnetized direction of therecording magnetic layer 25 as shown in FIG. 6A. The surrounding of theperpendicularly magnetized portion of the recording magnetic layer 25keeps an intra-plane magnetized status in which the magnetic axis isparallel to the layer surface to function as a mask 29 in which no Kerreffect will take place while the perpendicularly magnetized portionfunctions as an aperture 30 for the light beam L₁ incident upon therecording magnetic layer 25, as shown in FIG. 6B. Thus. since only theportion of the recording layer 22 on which the light beam L₁ is focusedis perpendicularly magnetized along the magnetized direction of therecording magnetic layer 25, it is possible to read, with highresolution, an information signal recorded in the form of microscopicpits 32 on recording tracks 31 formed with a small pitch on the opticaldisc 1.

In this embodiment, the first optical disc 1 has the diameter R₁ of 64mm and the thickness D₁ of 0.6 mm. However, the present invention is notlimited to these dimensions, but the diameter R₁ may be increased up to65 mm. The diameter R₁ may be 65 mm or less so long as an intendedstorage capacity can be attained. Also, the thickness D₁ of the opticaldisc 1 may appropriately be selected from a range of 0.4 to 0.7 mmdepending upon the wavelength of a light beam used to write and/or readthe information signal.

In addition to the first optical disc 1 as described in the foregoing,the present invention provides also another embodiment of an opticaldisc.

Referring now to FIG. 7, there is schematically illustrated a secondoptical disc according to the present invention. The optical disc isgenerally indicated with a reference 41. This optical disc 41 can beused in an optical recording and/or reproducing apparatus in which theaforementioned optical disc 1 can also be used. The optical disc 41 hasthe same construction as the optical disc 1 except for its outsidediameter. Therefore, the same or similar elements as or to those of theoptical disc 1 are indicated with the same or similar references andwill not further be described.

The optical disc 41 is formed to have a diameter of more than 38 mm toless than 52 mm and a thickness of 0.4 mm to 0.7 mm. More specifically,the optical disc 41 has a diameter R₁₁ of 50 mm as shown in FIG. 7. Theoptical disc 41 comprises a substrate 42 formed from glass or a lighttransparent polycarbonate resin having a signal recording layer formedon one side thereof.

The substrate 42 of the optical disc 41 is formed from a polycarbonateresin to have the diameter R₁₁ of 50 mm and a thickness D₁₁of 0.6 mm asshown in FIG. 7. The substrate 42 has formed at the center thereof acenter hole 3 having a diameter R₂ of 8 mm as in the optical disc 1. Thesubstrate 42 has formed around the center hole 3 an annulartable-abutment 4 being convex to one side of the substrate 42. There isprovided at the center of the substrate 42 a magnetic clamping hub 5 toclose the center hole 3 as in the optical disc 1. As shown, the hub 5consists of a depressed portion 6 formed at the center thereof. Thedepressed portion 6 has formed therein at the center thereof a spindlehole 8 in which engages a spindle of a rotation driving mechanism. Thespindle hole 8 has a diameter R₄ of 2.0 mm. As in the optical disc 1,the hub 5 is fitted at the depressed portion 6 thereof in the centerhole 3 of the substrate 2, and the table-abutment 4 is concaved asindicated with a reference 9 in its convexing direction. The hub 5 has aflange 7 formed around the depressed portion 6 thereof and which is tobe engaged in the concavity 9 of the substrate 42.

The substrate 42 has provided on the other side thereof, opposite tothat where the table-abutment 4 is formed, a signal recording layer 21,which is similar to that in the optical disc 1.

To write an audio and video information signal to the signal recordinglayer 21 of the optical disc 41, constructed as above-mentioned,pulse-irradiated magnetic modulation, in which a light beam is pulsedfor each recording data clock to modulate the recording magnetic fieldaccording to the recording data, is adopted as with the optical disc 1.

As in the optical disc 1, the optical disc 41 has the table-attachment 4provided at the center thereof as mentioned above. The recording and/orreproducing apparatus, which is compatible with both the optical discs 1and 41, has disposed therein a disc table 14 having the generally samesize as the table-attachment 4 and on which the table-attachment 4 is tobe mounted. Thus, the optical pickup unit compatible with the opticaldisc 1 will be used with the optical disc 42. Therefore, similarly tothe optical disc 1, the optical disc 41 will have formed thereon aninformation signal recording area extending outwardly from an insidediameter R₅ of at least 22 mm. Namely, the optical disc 41 has a signalrecording area extending outwardly from a radial position of 12.5 mm orless from the center of the optical disc 41, namely, from a diametricalposition R₆ of 25 mm or less, as shown in FIG. 7, to positively write amaximum amount of information signal.

More specifically, the optical disc 41 has defined thereon an audio andvideo information signal recording area of which the inside diameter R₆is 24.5 mm and the outside diameter R₁₇ is 46.5 mm. Further, on theoptical disc 41 are formed, inside the signal recording area, an area inwhich control signals, etc., which are used for information signal writeto and read from the optical disc 1, are recorded; and, outside thesignal recording area, an area in which control signals, etc., which areindicative of the end of the signal recording area, are recorded.

If pulse-irradiated magnetic modulation is adopted with the optical disc41 according to the present invention, use of a light beam of 400 nm inwavelength λ permits recording of 2 gigabytes or more of an informationsignal, while use of a light beam of 660 nm in wavelength λ permitsrecording of 1 gigabytes or more of an information signal.

To read an information signal recorded on the optical disc 41 using thepulse-irradiated magnetic modulation as described in the above, the samemethod as that for reading an information signal recorded on the opticaldisc 1 is adopted.

In the second embodiment, the second optical disc 41 has the diameterR₁₁ of 50 mm and the thickness D₁₁ of 0.6 mm. To assure an intendedstorage capacity of the optical disc 41, however, the diameter R₁₁, mayappropriately be selected from a range of 38 to 52 mm while thethickness D₁₁ may appropriately be selected from a range of 0.4 to 0.7mm depending upon the wavelength of a light beam used for write and/orread of an information signal.

In the foregoing, the first and second optical discs 1 and 41 accordingto the present invention have been described. Each of the optical discs1 and 41 has only a single signal recording layer on each of thesubstrates 2 and 42. However, in case the optical discs 1 and 41 areread-only optical discs, two or more signal recording layers may beformed on each of the substrates 2 and 42.

Referring now to FIG. 8, there is schematically displayed a thirdoptical disc, which is a read-only optical disc having two signalrecording layers. The optical disc is generally indicated with areference 111. The optical disc 111 is formed to have the same size asthe first optical disc 1. Its diameter is 65 mm or less and itsthickness ranges from 0.4 to 0.7 mm.

Similar to the optical disc 1, the optical disc 111 may have a diameterof up to 65 mm. It may have a diameter of 65 mm or less depending uponan intended storage capacity. Also the optical disc 111 is formed tohave a thickness appropriately selected from a range of 0.4 to 0.7 mmaccording to the wavelength of a light beam used to read an informationsignal recorded on the optical disc 111.

As shown in FIG. 8, the third optical disc 111 comprises a substrate 112formed from a light-transparent synthetic resin such as polycarbonate.The substrate 112 is formed to have a diameter of 65 mm or less and athickness D₂₁ ranging from 0.4 to 0.7 mm. It has preformed on one sidethereof a pit pattern 113 that is a pattern of very small convexitiesand concavities. That is to say, the substrate 112 is formed byinjecting a molten polycarbonate into a mold in which there is disposeda stamper having formed thereon a pattern of convexities and concavitiescorresponding to the concavities and convexities, respectively, on thepit pattern 113. As shown in FIG. 8, the substrate 112 has a firstsignal recording layer 114 formed along the pit pattern 113 on one sidethereof where the pit pattern 113 is formed. The first signal recordinglayer 114 is formed from a translucent silicon film such as Si₃N₄, SiO₂or the like which allows to pass a predetermined amount of a light beamirradiated through the substrate 112 while reflecting a predeterminedamount of the light beam. The first signal recording layer 114 consistsof more than one silicone film of Si₃N₄, SiO₂ or the like stacked one onthe other to a thickness D₂₂ of 100 to 500 nm. The silicon films ofSi₃N₄, SiO₂ or the like are produced by vacuum deposition or sputtering.

In this read-only optical disc 111, the pit pattern 113 formed on thesubstrate 112 is formed with a track pitch about 1.4 times larger thanthat of the recording tracks formed on the optical discs 1 and 41. Also,the minimum length of the pits included in the pit pattern 113 is about1.4 times larger than those in the optical discs 1 and 41. That is, inthe read-only optical disc 111, the track pitch of the recording tracksis 0.4 to 0.77 μm and pit length is 0.14 to 0.31 μm/bit. Therefore, therecording tracks can be formed by injection molding of a syntheticresin.

When formed to sizes for the discs 1 and 41, respectively, the stamperprepared with the above-mentioned track pitch and shortest pit lengthwill provide a pit pattern being a half of that recorded on the opticaldiscs 1 and 41. The pit pattern will result in a storage capacity of thesubstrate 112 that is also a half of that of the discs 1 and 41.Therefore, when the stamper in consideration is used to form the opticaldisc 111 in a size corresponding to that of the discs 1 and 41, theamount of information recordable on this optical disc 111 will be a halfof that recordable on the optical discs 1 and 41.

In the optical disc 111, the substrate 112 has a center hole 3 formed atthe center thereof, as in the optical discs 1 and 41. The substrate 112has formed around the center hole 3 and on a side thereof, opposite tothe side on which the signal recording layer 114 is formed, an annulardisc-abutment 4 convexing away from the signal recording layer 114.Further, a magnetic-clamping hub 5 is provided at the center of thesubstrate 112 to close the center hole 3, as in the optical discs 1 and41.

To the first signal recording layer 114 on the substrate 112 of theoptical disc 111, there is joined a sheet 116 formed sufficientlythinner than the substrate 112 and having preformed on one side thereofa pit pattern 115 being a pattern of very small concavities andconvexities corresponding to information signals. There is providedbetween the first signal recording layer 114 and sheet 116 alight-transparent layer 117 made of a light-transparentultraviolet-curable synthetic resin.

The sheet 116 is formed from a light-transparent synthetic resin such aspolycarbonate to a thickness D₂₃ of 0.05 to 0.1 mm. The pit pattern 115formed on one side of the sheet 116 is formed by thermally stamping apattern formed on a stamper and consisting of convexities andconcavities corresponding to the concavities and convexities,respectively, of the pit pattern 115. As shown in FIG. 8, a secondsignal recording layer 118 is formed along the pit pattern 115. Toreflect with a high efficiency towards an optical pickup unit disposedin front of the substrate 112, a light beam focused thereon through thefirst signal recording layer 114 and light-transparent layer 117, thesecond signal recording layer 118 is formed from a film of a highlyreflective metal such as aluminum (Al), gold (Au) or silver (Ag).

The sheet 116 having the pit pattern 115 and second signal recordinglayer 118 formed thereon is produced through a process as shown in FIG.9. To form the sheet 116, a polycarbonate web 121 is fed to areplicating or stamping post where a stamper 122 and pressing roller 124are provided. The stamper 122 has formed thereon a pattern 123 ofconcavities and convexities corresponding to the convexities andconcavities, respectively, of the intended pit pattern 115. The pressureroller 124 is provided with a heating means. The polycarbonate web 121is passed between the stamper 122 and pressure roller 124 while beingheated and pressed. Thus, the polycarbonate web 121 has the pit pattern123 stamped thereon, and is further fed towards a take-up roll 121 a.Before the polycarbonate web is taken up on the roll 121 a, it is movedinto a sputtering post where the second signal recording layer 118 isformed on a portion of the web 121 on which the pit pattern 123 has beenstamped. Further, the polycarbonate web 122 is moved to a punching postwhere the web portion, on which the second signal recording layer 118 isformed, is punched to a size for attachment to the substrate 112,thereby forming the sheet 116. The web 122 is wound on a take-up roll121 a.

The pit pattern 123 formed on the stamper 122 is formed on recordingtracks whose pitch is about 1.4 times larger than that of the recordingtracks formed on the optical discs 1 and 41. The minimum length of thepits forming the pit pattern 115 is also about 1.4 times larger thanthat in the optical discs 1 and 41. When the stamper 122 for such tackpitch and minimum pit length is formed to sizes corresponding to thoseof the optical discs 1 and 41, respectively, it will have a pit patternbeing a half of those of the pit patterns formed on the optical discs 1and 41, and whose storage capacity is also a half of those of theoptical discs 1 and 41. When the sheet 116 formed by the stamper 122 isformed to sizes corresponding to those of the optical discs 1 and 41,respectively, the amount of information recorded on the sheet 116 willbe a half of those of the optical discs 1 and 41.

The sheet 116 thus formed is joined to the substrate 112 with the secondand first signal recording layers 118 and 114 placed face-to-face. Asmentioned above, an ultraviolet-curable resin is used as thelight-transparent layer 117 between the sheet 116 and substrate 112.

To join the sheet 116 to the substrate 112, they are centered with eachother and the first and second signal recording layers 114 and 118 areplaced in a face-to-face relation with a space D₂₄ of 20 to 35 μmbetween them. To this end, a jig 125, for example, is inserted into acenter hole 116 a formed at the center of the sheet 116 and center hole3 in the substrate 112 as shown in FIG. 10 to center the sheet 116 andsubstrate 112 with each other and to provide the space of 20 to 35 μmbetween the first and second signal recording layers 114 and 118. Thenan ultraviolet-curable resin, for example, is injected between thesubstrate 112 and sheet 116 to form the light-transparent layer 117.With the substrate 112 and sheet 116 rotated, the ultraviolet-curableresin injected between the substrate 112 and sheet 116 is spread to auniform thickness. Thereafter, ultraviolet rays are irradiated throughthe substrate 112 to harden the ultraviolet-curable resin to join thesubstrate 112 and sheet 116 to each other.

Next, the hub 5 is installed to the substrate 112 to cover the centerhole 3 in the substrate 112 to finish the optical disc 111.

As mentioned above, the substrate 112 and sheet 116 are joined to eachother with the space of 20 to 35 μm between them and theultraviolet-curable resin, for example, injected into the space to formthe light-transparent layer 117 which will thus have a thickness D₂₄ of20 to 35 μm.

When a light beam of 380 to 420 nm in wavelength λ, or a light beam of630 to 670 nm in wavelength λ, is focused on the first or second signalrecording layer 114 or 118 through an objective lens having a numericalaperture (NA) of 0.5 to 0.7, the focal depth will be ±1 μm. Since thelight-transparent layer 117 has the thickness D₂₄ of 20 to 35 μm, aninformation signal recorded on the first or second signal recordinglayer 114 or 118 can accurately be read by a common light beam L₂ andobjective lens 131 independently without mutually affecting each otherand without being influenced by a spherical aberration of the objectivelens 131.

To read an information signal from the first or second recording layer114 or 118, the position of the objective lens 131 is controlled for thelight beam L₂ to be focused on the first or second signal recordinglayer 114 or 118 as shown in FIG. 8. The position of the objective lens131 is controlled using, for example, control signals indicative of thefirst and/or second signal recording layers 114 and/or 118 and recordedin control signal recording areas for the first and/or second signalrecording layers 114 and/or 118.

In the aforementioned third optical disc 111 according to the thirdembodiment, an information signal can be recorded on each of the firstand second signal recording layers 114 and 115 in an amount being a halfof that recordable in the optical disc 1. Therefore, the optical disc111 has a total storage capacity equivalent to that of the optical disc1.

As in the above, the read-only optical disc 111 is constructed so thatan information signal is read from the first and second signal recordinglayers 114 and 118 by irradiating light beams through the substrate 112to the respective signal recording layers 114 and 118. However, byforming the second signal recording layer 118 from a translucentmaterial which will allow to pass a predetermined amount of a light beamwhile reflecting a predetermined amount of the light beam, it is alsopossible to read information signal from the first and second signalrecording layers 114 and 118 by irradiating a light beam through thesheet 116.

Further, in the read-only optical disc 111, a second sheet 126 may bejoined to the sheet 116 (namely, the first sheet) with a secondlight-transparent layer 127 made of a light-transparent,ultraviolet-curable material or the like laid between them as shown inFIG. 11. Namely, three signal recording layers may be formed in theoptical disc 111. In this case, the signal recording layer 118 formed onat least the first sheet 116 is formed as a translucent layer which willallow to pass a predetermined amount of a light beam while reflecting apredetermined amount of the light beam.

The above-mentioned read-only multi-layered optical disc may be formedto the size of the second optical disc according to the presentinvention, that is, the optical disc 41. Also in this case, since eachof the signal recording layers is able to record a half of theinformation amount recordable on the optical disc 41, the two signalrecording layers can record a total amount of information equivalent tothat recordable in the first optical disc according to the presentinvention, namely, the optical disc 1.

The optical discs 1 and 41 constructed as having been described in theforegoing record an information signal with an extremely high density.Therefore, any little dust or small scratch on the optical discs willmake it impossible to accurately write or read an information signal.

Thus, to avoid the above inconvenience, each of the optical discs 1 and41 according to the present invention is encased in a cartridge. As adisc cartridge, it is set as encased in a cartridge in a recordingand/or reproducing apparatus or it is stored as encased in thecartridge.

Referring now to FIGS. 12 to 19, there are illustrated disc cartridgesaccording to the present invention.

The disc cartridge is generally indicated with a reference 51 as shownin FIGS. 12 and 13. The disc cartridge 51 encases the optical disc 1having been described in the foregoing. It consists of upper and lowerhalves 52 and 53 butted to each other to form a cartridge 54 in whichthe optical disc 1 is encased. The cartridge 54 is formed to have arectangular shape of which a first side has a length W₁ of 52 to 70 mmand a second side has a length W₂ of 52 to 75 mm, perpendicular to thefirst side. Therefore, the optical disc 1 of 65 mm or less in diametercan be encased rotatably in the cartridge 54. The lengths W₁ and W₂ ofthe first and second sides of the cartridge 54 are appropriatelyselected from ranges of 52 to 70 mm and 52 to 75 mm, respectively,according to the size of the optical disc 1 to be encased in thecartridge 54. The cartridge 54 has a thickness D₃ selected from a rangeof 3 to 6 mm according to the thickness of the optical disc 1 to beencased therein.

That is, the cartridge 54 is formed according to the size of the opticaldisc 1 to have a rectangular shape having a necessary minimum length,width and thickness to encase the optical disc 1.

In effect, the disc cartridge 51 shown in FIGS. 12 and 13 comprises thecartridge 54 with the first side having the length W₁ of 68 mm, secondside having the length W₂ of 72 mm and thickness D₃ of 5 mm since theoptical disc 1 to be encased therein has a diameter R₁ of 64 mm andthickness D₁ of 0.6 mm.

The cartridge 54 has formed in the upper half 52 thereof a writingaccess opening 55 through which a radially extending part of the opticaldisc 1 encased therein is exposed. The writing access opening 55 isprovided to allow an external field-applying magnetic head of arecording and/or reproducing apparatus to approach the optical disc 1for writing of an information signal to the latter. The writing accessopening 55 is formed to a rectangular shape extending from near a centerof the cartridge 54 to near a shorter front side of the cartridge 54.The writing access opening 55 is located with its longitudinal axispassing through the center of the optical disc 1 and a middle point P₁of the front side width of the cartridge 54.

Also, the lower half 53 of the cartridge 54 has formed therein areading/writing access opening 56 through which a radially extendingpart of the optical disc 1 encased therein is exposed and which allowsan optical pickup unit of a recording and/or reproducing apparatus toapproach the optical disc 1 for writing and reading of an informationsignal to and from the latter, and a central opening 57 through whichthe table-abutment 4 provided at the center of the optical disc 1 isexposed. The central opening 57 is formed at the center of the lowerhalf 53, and the reading/writing access opening 56 is formedcontiguously to the central opening 57 to have a rectangular shapeextending to near the front side of the cartridge 54. As shown in FIG.13, the reading/writing access opening 56 has a middle point P₂ of thewidth thereof deviated from the middle point P₁ of the front side widthof the cartridge 54 towards one of the lateral sides of the cartridge54. Owing to this deviation of the reading/writing access opening 56from the center of the cartridge 54, the main body of the optical pickupunit can be displaced from the center line of the optical disc 1 withthe optical axis of the objective lens positioned on the center line ofthe optical disc 1, so that the recording and/or reproducing apparatuscompatible with the disc cartridge 51 can be designed more compact.

The cartridge 54 is provided with a shutter member 58 to open and closethe writing access opening 55, reading/writing access opening 56 andcentral opening 57 at the same time. The shutter member 58 is made bypunching and bending a thin metal sheet. It consists of a first shutterportion 59 to open and close the writing access opening 55, secondshutter member 60 to open and close the reading/writing access opening56 and central opening 57, and a juncture 61 to connect the bases of thefirst and second shutter portions 59 and 60. The shutter member 58 isformed to have a generally C-shaped cross-section. The juncture 61 hasfirst and second projecting sliding guides 62 and 63 fitted on the frontside of the cartridge 54. As shown in FIG. 12, the first shutter portion59 is formed to have a rectangular shape having sufficient dimensions toclose the writing access opening 55. As shown in FIG. 13, the secondshutter portion 60 extends from the juncture 61 while being deviatedlaterally in relation to the first shutter portion 59 to close both thereading/writing access opening 56 formed off the center of the cartridge54 and the central opening 57 formed at the center of the cartridge 54.Also the second shutter portion 60 is bent to close the central opening57 which is positioned off the longitudinal axis of the reading/writingaccess opening 56.

The shutter member 58 is fitted onto the cartridge 54 with the firstshutter portion 59 laid over the writing access opening 55 and thesecond shutter portion 60 laid over the reading/writing access opening56 and central opening 57. At this time, the first and second slidingguides 62 and 63 of the shutter member 58 are engaged on the front sideof the cartridge 54 with guide pieces thereof (not shown) engaged insliding guide recesses, respectively, formed in the cartridge 54. Theshutter member 58 thus installed on the cartridge 54 can be preventedfrom slipping off on the cartridge 54, and can be moved along the frontsurface of the cartridge in the directions of arrows A and B in FIGS. 12and 13 to open and close the writing access opening 55, reading/writingaccess opening 56 and central opening 57 simultaneously.

There is provided inside the cartridge 54 a locking member (not shown)which engages with the shutter member 58 having been moved to a positionwhere it closes the writing access opening 55, reading/writing accessopening 56 and central opening 57, to thereby hold the shutter member 58in that position. When the shutter member 58 is in the closed position,the locking member engages with a locking piece provided on the firstsliding guide 62 to keep the shutter member 58 in the closed position.

When the disc cartridge 51 is ejected from a recording and/orreproducing apparatus, the shutter member 58 is held by a shutterholding member and moved in relation to the cartridge 54 to a positionwhere it closes the reading/writing access opening 56 and centralopening 57. Therefore, the disc cartridge 51 needs no forcing means suchas a spring to move the shutter member 58 to the closed position.

The second shutter portion 60 formed long enough to close thereading/writing access opening 56 and central opening 57 has a free endthereof supported by a moving guide piece 60 a fixed on the lowersurface of the cartridge 54 as shown in FIG. 13. Thus the second shutterportion 60 is prevented from floating from the lower surface of thecartridge 54 and can positively close the central opening 57.

The cartridge 54 has formed on the front side thereof an engagementrecess 64 in which a shutter releasing member provided in a recordingand/or reproducing apparatus is engaged when the disc cartridge 51 isset in the recording and/or reproducing apparatus. The engagement recess64 is open at one end thereof at which the disc cartridge 51 is firstintroduced into the recording and/or reproducing apparatus.

When the disc cartridge 51 thus constructed is introduced into arecording and/or reproducing apparatus first at one lateral side thereofat which the engagement recess 64 is open, namely, in the direction ofarrow E in FIGS. 12 and 13, the shutter releasing member of therecording and/or reproducing apparatus enters the engagement recess 64,and presses to displace the locking member, thereby disengaging thelatter from the locking piece of the shutter member 58. As the disccartridge 51 is further inserted into the recording and/or reproducingapparatus after the locking piece is disengaged from the locking member,the cartridge 54 is moved while the shutter member 58 is restricted bythe shutter releasing member from moving, so that the writing accessopening 55, reading/writing access opening 56 and central opening 57 areopened. Thus the disc cartridge 51 is set in place in the recordingand/or reproducing apparatus.

As shown in FIG. 13, the cartridge 54 has formed on the lower surfacethereof first and second positioning holes 65 and 66 for receivingpositioning pins provided in the recording and/or reproducing apparatus.The positioning holes 65 and 66 are formed in positions at the frontcorners, respectively, of the cartridge 54 at which the holes 65 and 66are not opposite to the optical disc 1 encased in the cartridge 54.

The first disc cartridge 51 constructed as described in the above isformed to have a sufficient size to encase the optical disc 1 having asmall diameter. The reading/writing access opening 56 is formed nearerto one lateral side of the cartridge 54. Therefore, along with thecompact design of the disc cartridge 51, the recording and/orreproducing apparatus in which the disc cartridge 51 is to be used canbe designed correspondingly compact.

Referring now to FIGS. 14 and 15, there is illustrated a second disccartridge according to the present invention, designed to encase thesecond optical disc according to the present invention, namely, theoptical disc 41. The disc cartridge is generally indicated with areference 71.

Similar to the first disc cartridge, namely, the disc cartridge 51having been described in the foregoing, the disc cartridge 71 consistsof an upper half 72 and lower half 73 butted to each other to form acartridge 74 in which the disc cartridge 41 is to be encased. Thecartridge 74 is formed to have a rectangular shape of which a first sidehas a length W₁ of 41 to 57 mm and a second side has a length W₂ of 41to 62 mm, perpendicular to the first side. Therefore, the optical disc41 of more than 38 mm and 52 mm or less in diameter can be encasedrotatably in the cartridge 74. The lengths W₁, and W₂ of the first andsecond sides of the cartridge 74 are appropriately selected from rangesof 41 to 57 mm and 41 to 62 mm, respectively, according to the size ofthe optical disc 1 to be encased in the cartridge 54. The cartridge 54has a thickness D₄ selected from a range of 3 to 6 mm according to thethickness of the optical disc 41 to be encased therein.

That is, the cartridge 74 is formed according to the size of the opticaldisc 41 to have the rectangular shape having minimum necessary length,width and thickness to encase the optical disc 41.

In effect, the disc cartridge 71 shown in FIGS. 14 and 15 comprises thecartridge 74 with a first side having a length W₃ of 54 mm, second sidehaving a length W₄ of 57 mm and thickness D₄ of 5 mm, since the opticaldisc 41 to be encased therein has a diameter R₁₁ of 50 mm and thicknessD₁₁ of 0.6 mm.

As in the disc cartridge 51, the cartridge 74 has formed in the upperhalf 72 thereof a writing access opening 75 through which a radiallyextending part of the optical disc 41 encased therein is exposed. Also,the lower half 73 of the cartridge 74 has formed therein areading/writing access opening 76 through which a radially extendingpart of the optical disc 41 encased therein is exposed and which allowsan optical pickup unit of a recording and/or reproducing apparatus toapproach the optical disc 41 for writing and reading of an informationsignal to and from the latter, and a central opening 77 through whichthe table-abutment 4 provided at the center of the optical disc 41 isexposed. Similarly to the reading/writing access opening in the disccartridge 51, the reading/writing access opening 76 has a middle pointP₄ of the width thereof deviated from the middle point P₃ of the frontside width of the cartridge 74 towards one of the lateral sides of thecartridge 74, as shown in FIG. 15.

The cartridge 74 is provided with a shutter member 78 to open and closethe writing access opening 75, reading/writing access opening 76 andcentral opening 77 at the same time. The shutter member 78 isdimensioned differently from the shutter member of the disc cartridge 51but constructed similarly to the latter. So, the same or similarelements as or to those of the shutter member of the disc cartridge 51are indicated with the same reference numerals used for the latter andwill not be described in further detail.

The cartridge 74 of the disc cartridge 71 has formed on the front sidethereof an engagement recess 84 in which a shutter releasing memberprovided in a recording and/or reproducing apparatus is engaged when thedisc cartridge 71 is set in the recording and/or reproducing apparatus.The engagement recess 84 is open at one end thereof at which the disccartridge 71 is first introduced into the recording and/or reproducingapparatus.

When the disc cartridge 71 thus constructed is introduced into arecording and/or reproducing apparatus first at one lateral side thereofat which the engagement recess 84 is open, the shutter releasing member(not shown) of the recording and/or reproducing apparatus enters theengagement recess 84, and presses to displace the locking member (notshown), thereby disengaging the latter from the locking piece (notshown) of the shutter member 78. As the disc cartridge 71 is furtherinserted into the recording and/or reproducing apparatus after thelocking piece is disengaged from the locking member, the cartridge 74 ismoved while the shutter member 78 is restricted by the shutter releasingmember from moving, so that the writing access opening 75,reading/writing access opening 76 and central opening 77 are opened.Thus the disc cartridge 71 is set in place in the recording and/orreproducing apparatus.

As shown in FIG. 15, the cartridge 74 has formed on the lower surfacethereof first and second positioning holes 85 and 86 in whichpositioning pins provided in the recording and/or reproducing apparatusare engaged when the disc cartridge 71 is set in the recording and/orreproducing apparatus. The positioning holes 85 and 86 are formed inpositions at the front corners, respectively, of the cartridge 74 atwhich the holes 85 and 86 are not opposite to the optical disc 41encased in the cartridge 74.

The disc cartridge 71 is designed smaller than the disc cartridge 51since it is used to encase the optical disc 41 smaller than the opticaldisc 1. However, since the optical discs 1 and 41 are identical to eachother in the method of attaching each of them to the rotation drivingmechanism of a recording and/or reproducing apparatus and the method ofwriting and reading an information signal to and from their signalrecording layers, it is desirable for both the disc cartridges 51 and 71to be usable commonly in the recording and/or reproducing apparatuswhich is compatible with at least the disc cartridge 51.

For selective use of the disc cartridges 51 and 71 of different sizes ina common recording and/or reproducing apparatus, it is necessary toprovide the apparatus with a cartridge receiver or holder which canselectively position each of the disc cartridges 51 and 71 forattachment to the rotation driving mechanism.

A recording and/or reproducing apparatus for optical discs as recordingmedia comprises an optical pickup unit and magnetic head unit movingover the upper and lower surfaces of the optical disc. Therefore, it isdifficult to additionally provide a disc cartridge positioning mechanismwithin the reach of the optical pickup unit and magnetic head unit.

In such a situation, it should desirably be possible with only a minormodification of a recording and/or reproducing apparatus in which thedisc cartridge 51 is usable, to set the disc cartridge 71 in place inthe apparatus in a similar manner to that for setting the disc cartridge51.

To this end, the present invention provides also an adapter for use withboth the disc cartridges 51 and 71 commonly in a recording and/orreproducing apparatus. FIGS. 16 to 18 show together the adapter. Theadapter is generally indicated with a reference 91 and has the same sizeas the disc cartridge 51.

As shown in FIG. 16, the adapter 91 is designed to have a rectangularshape whose outside dimensions are same as those of the cartridge 54 ofthe disc cartridge 51. The adapter 91 has formed in the center thereof acartridge holding concavity 92 to receive the disc cartridge 71. Theconcavity 92 has a sufficient size to receive the disc cartridge 71. Theadapter 91 has formed, on the bottom of the concavity 92, first andsecond positioning pins 93 and 94, which engage the first and secondpositioning pin engagement holes 85 and 86, respectively, formed in thedisc cartridge 71, as shown in FIGS. 16 and 17. Further, first andsecond projections 95 and 96 are formed on the bottom of the concavity92 along a wall of the concavity 92 opposite to the wall along which thepins 93 and 94 are provided. The first and second projections 95 and 96are provided to support the lower surface of the disc cartridge 71 andto level the latter in relation to the adapter 91.

Moreover, there is formed in the bottom of the concavity 92 an opening97 through which the reading/writing access opening 76 and centralopening 77, which is formed in the lower half of the disc cartridge 71received in the adapter 91, are exposed.

Furthermore, the adapter 91 has provided at the front side thereof ashutter coupling member 98 which is connected to the shutter member 78of the disc cartridge 71 set in the adapter 91. The shutter couplingmember 98 is provided with an engagement projection 99 for engagement inthe engagement hole 61 a formed in the juncture 61 of the shutter member78. The shutter member 78 is installed movably along the front side ofthe adapter 91 in the directions of arrows C and D in FIG. 16, which isthe same as the moving direction of the shutter member 78. The shuttercoupling member 98 is also provided with an engagement piece 100, whichwill be engaged with the shutter releasing member engagement recess 84formed in the disc cartridge 71 set on the cartridge holding concavity92.

Further, the adapter 91 has formed along the front side thereof ashutter releasing member engagement recess 101 similar to the shutterreleasing member engagement recess 64 formed along the front side of thedisc cartridge 51.

Moreover, the adapter 91 has formed on the lower surface thereof firstand second positioning pin engagement holes 102 and 103 in positions,respectively, corresponding to the first and second positioning pinengagement holes 65 and 66 of the disc cartridge 51.

As shown in FIG. 18, the disc cartridge 71 is received in the adapter 91thus constructed with the engagement projection 99 engaged in theengagement hole 61 a of the shutter member 78, the engagement piece 100engaged in the shutter releasing member engagement recess 84 and thefirst and second positioning pins 93 and 94 engaged in the first andsecond engagement holes 85 and 86, respectively. The disc cartridge 71thus received in the adapter 91 will have the same shape as the disccartridge 51. Namely, it can be handled similarly to the disc cartridge51.

That is to say, the adapter 91 with the disc cartridge 71 set in thecartridge holding concavity 92 is introduced, first at the lateral sidethereof perpendicular to the front side on which the shutter couplingmember 98 is installed, into a recording and/or reproducing apparatus.As the adapter 91 is further inserted into the recording and/orreproducing apparatus, the shutter releasing member provided on therecording and/or reproducing apparatus enters the shutter releasingmember engagement recess 101 to move the shutter coupling member 98 inthe direction of arrow C in FIG. 18. As the shutter coupling member 98is moved in the direction of arrow C in FIG. 18, the engagement piece100 provided on the shutter coupling member 98 moves in the shutterreleasing member engagement recess 84 of the disc cartridge 71 in thedirection of arrow C to press and displace the locking member providedinside the disc cartridge 71. Thus the locking member is disengaged fromthe locking piece provided on the shutter member 78. As the adapter 91is inserted further into the reading and/or reproducing apparatus afterthe disengagement of the locking member from the locking piece, thecartridge 74 is moved along with the adapter 91 with the shutter member78 restricted by the engaging piece 100 from moving, so that the writingaccess opening 75, reading/writing access opening 76 and central opening77 are opened. Thereafter, the adapter 91 is set together with the disccartridge 71 held therein onto a cartridge mount in the recording and/orreproducing apparatus. The adapter 91 is correctly positioned on thecartridge mount since positioning pins provided in the recording and/orreproducing apparatus are engaged in the first and second positioningpin engagement holes 102 and 103, respectively.

It should be noted that to selectively set the disc cartridges 51 and 71of different sizes in the recording and/or reproducing apparatus, acartridge mount in which each of the disc cartridges 51 and 71 can beheld may be provided in the apparatus. In this case, the cartridge mountis provided with positioning pins which are to be engaged in the firstand second positioning pin engagement holes 65 and 66 in the disccartridge 51, respectively, and those which are to be engaged in thefirst and second positioning pin engagement holes 85 and 86,respectively. To make it possible to selectively set the disc cartridges51 and 71 in the recording and/or reproducing apparatus, there areformed in the disc cartridge 51, larger than the disc cartridge 71,relief holes in which the positioning pins are to be received in thefirst and second positioning pin engagement holes 85 and 86,respectively, in the disc cartridge 71.

As having been described in the foregoing, since the disc cartridges 51and 71 encase the write/read optical discs 1 and 41, respectively, whichare capable of recording an information signal, the cartridges 54 and 74have formed in the upper half thereof the writing access openings 55 and75 through which a magnetic head writes information to the respectiveexposed optical discs 1 and 41. However, a disc cartridge in which theread-only optical disc 111 is encased has no writing access openingformed in the upper half thereof, while having formed in the lower halfthereof only a reading access opening, through which the optical pickupunit is exposed and a central opening through which the table-abutmentthereof is exposed. Therefore, the disc cartridge encasing the read-onlyoptical disc may have only a shutter for the reading access opening andcentral opening formed in the lower half thereof.

The disc cartridge 51 encasing the optical disc 1 and the disc cartridge71 encasing the optical disc 41 are set in a recording and/orreproducing apparatus constructed as will be described below, to writeand read information signal to and from the optical discs 1 and 41.

As mentioned above, the disc cartridge 71 is set in the adapter 91 andset as it is in the recording and/or reproducing apparatus. Similarly tothe disc cartridges 51 and 71, the cartridge in which the read-onlyoptical disc 111 is encased may be set in the recording and/orreproducing apparatus to read information signal recorded on the opticaldisc 111.

Referring now to FIG. 19, there is schematically displayed a recordingand/or reproducing apparatus in which each of the disc cartridges 51 and71 and a disc cartridge encasing the read-only optical disc 111 isusable. The recording and/or reproducing apparatus is generallyindicated with a reference 200. As shown, the disc cartridge 51, thedisc cartridge 71 set in the adapter 91 or the disc cartridge encasingthe read-only optical disc 111 is set in the recording and/orreproducing apparatus 200 to write information signals such as audiosignal, video signal, etc. and read an information signal recorded inthe optical disc. The recording and/or reproducing apparatus 200comprises a magnetic head unit to apply an external magnetic field tothe magneto-optical disc when writing information signal to the latter.

As shown in FIG. 19, the recording and/or reproducing apparatus 200comprises a housing, a flat, generally rectangular base 201 formed froma metallic material and disposed in the housing, and a cartridge holder202 to hold a disc cartridge. The cartridge holder 202 is supportedpivotably on the base 201. The base 201 has incorporated therein arotation driving mechanism 11 which drives to spin the optical disc 1(41 or 111) and an optical pickup unit 203. There is provided on thebase 201 a cartridge mount 205 on which a disc cartridge (not shown)held in the cartridge holder 202 is set. The cartridge holder 202 hasdisposed thereon a magnetic head unit 206 which is moved synchronouslywith the optical pickup unit 204 radially of the optical disc 1.

The rotation driving mechanism 11 is constructed as having previouslybeen described with reference to FIG. 4.

As shown in FIG. 19, the optical pickup unit 204 comprises mainly asemiconductor laser to emit a light beam, an objective lens 131 to focusthe light beam emitted from the semiconductor laser onto the opticaldisc 1, a photodetector to detect a return light from the optical disc 1in order to detect an information signal and control signals, etc. Theoptical pickup unit 204 is supported at both sides thereof by a pair ofguide shafts 207 installed in parallel to each other on the bottom ofthe base 201 to be movable radially of the optical disc 1 set on thedisc table 14. The objective lens 131 faces the upper surface of thebase 201 and the optical disc 1 set on the disc table 14 through anopening 208 formed in the base 201. The optical pickup unit 204 isguided on the guide shafts 207 by a feed screw (not shown) driven by adrive motor (not shown) fixed on the bottom of the base 201, and thusmoved radially of the optical disc 1 on the disc table 14. That is, towrite or read an information signal, the optical pickup unit 204 ismoved radially from the lead-in area towards the lead-out area of theoptical disc 1.

As shown also in FIG. 19, the magnetic head unit 206 is linked with theoptical pickup unit 204, which writes an information signal to theoptical disc 1. Namely, the magnetic head unit 206 is also movedradially of the optical disc 1 on the disc table 14 as the opticalpickup unit 204 is so moved. The magnetic head unit 206 comprises amagnetic head 210 to apply to the optical disc 1 with an externalmagnetic field modulated according to an information signal to bewritten to the optical disc, and a magnetic head supporting plate 211provided with a leaf spring supporting at the free end thereof themagnetic head 210 and which can elastically be displaced. The magnetichead unit 206 is linked with the optical pickup unit 204 by a linkagemember 213 in such a manner that it is positioned in a position where itwill be opposite to the optical pickup unit 204 with the optical disc 1on the disc table 14 located between them.

As shown in FIG. 19, the linkage member 213 consists of a coupling piece215 and a fixture 216 formed by bending one end of the coupling piece215 perpendicularly to the latter itself and by which the linkage member213 is fixed to the optical pickup unit 204. The linkage member 213 isformed to have a generally L shape. The linkage member 213 is installedto the optical pickup unit 204 with the fixture 216 fixed to the opticalblock with fixing screws or the like so that the free end of thecoupling piece 215 projects above the base 201. The base end of themagnetic head supporting plate 211 is pivotably supported on the otherend of the coupling piece 215 by means of a pivot (not shown). Thus themagnetic head supporting plate 211 is pivotable about the pivot indirections of the magnetic head 210 supported at the free end of theplate 211 being turned towards and away from the optical disc 1 on thedisc table 14.

As the optical pickup unit 204 is driven by the feeding motor to moveradially of the optical disc 1, the magnetic head unit 206 thus coupledto the optical pickup unit 204 by means of the linkage member 213 isalso moved along with the optical pickup unit 204 radially of theoptical disc 1.

As shown in FIG. 19, the cartridge holder 202 in which the disccartridge is inserted and held is pivotally installed to the base 201 ina position between the base 201 and magnetic head unit 206. Thecartridge holder 202 has provided at opposite lateral sides thereofcartridge guides 221 and 222 to guide and hold a disc cartridge, andalso has a cartridge inlet 223 formed at the front side thereof. A disccartridge inserted from the cartridge inlet 223 into the cartridgeholder 202, is held at opposite lateral sides thereof by the cartridgeguides 221 and 222, respectively.

The recording and/or reproducing apparatus 200 with the rotation drivingmechanism 11 constructed as mentioned above works as will be describedbelow when the disc cartridge 51 encasing the optical disc 1, forexample, is set therein:

First, to write an information signal to the optical disc 1 or to readan information signal recorded on the optical disc 1, the cartridgeholder 202 is pivoted to its upper position where it is apart from thecartridge mount 205. At this time, the cartridge inlet 223 of thecartridge holder 202 will be directed to above the apparatus. Then, thecartridge holder 202 in which the disc cartridge is held is pivotedtowards the cartridge mount 205 and thus the disc cartridge 51 ispositioned in place on the cartridge mount 205.

At this time, the optical disc 1 in the disc cartridge 51 is set on thedisc table 14 of the rotation driving mechanism 11 and clamped there forrotation with the disc table 14. When it is detected that the disccartridge set on the cartridge mount 205 encases the optical disc 1 andthe write mode of operation is selected by using a record button, thespindle motor 12 is driven to spin forward and the optical disc 1 isspun along with the disc table 14. The optical pickup unit 204 is putinto operation. A light beam emitted from a light source scans over thesignal recording layer 21 of the optical disc from the lead-in to leadout while the magnetic head 210 applies the optical disc 1 with anexternal magnetic field modulated according to an information signal tobe written. Thus, a desired information signal is written to the opticaldisc 1.

When the read mode of operation is selected by using a play button, alight beam emitted from the semiconductor laser of the optical pickupunit 204 is irradiated to the signal recording layer 21 of the opticaldisc 1, a return light from the signal recording layer 21 of the opticaldisc 1 is detected by the photodetector of the optical pickup unit 204.Thus, an information signal is read from the optical disc 1. It shouldbe noted that for information signal reading, no external magnetic fieldmay be applied to the optical disc 1, namely, the magnetic head unit 206is not required.

In the above-mentioned recording and/or reproducing apparatus 200, theoptical pickup unit 204 emits a light beam which enables a high densityrecording as having previously been described. A semiconductor laseremitting a light beam of 380 to 420 nm in wavelength λ or a light beamof 630 to 670 nm in wavelength λ is used as the laser source. Theobjective lens 131 has a numerical aperture NA of 0.5 to 0.7 to permit ahigh resolution. The magnetic head 210 is a high frequency type one toenable a high density recording.

In addition to the first disc cartridge 51 encasing the first opticaldisc 1, the second disc cartridge 71 encasing the second optical disc 41or the disc cartridge in which the read-only optical disc 111 is encasedcan be used in the recording and/or reproducing apparatus to write orread an information signal in the same manner as mentioned above.

As having been described in the foregoing, since the optical recordingmedium and the disc cartridge encasing the optical recording mediumaccording to the present invention are very compact and able to anrecord information signal with a high density, a recording and/orreproducing apparatus can be provided which is correspondingly compactand can write or read an information signal such as audio and videoinformation for a sufficiently long time.

Although modifications and changes may be suggested by those of ordinaryskill in the art, it is the intention of the inventors to embody withinthe patent warranted hereon all changes and modifications as reasonablyand properly come within the scope of their contribution to the art.

We claim as our invention:
 1. A disc cartridge in which a read-writerecording medium is encased, the read-write recording medium including adisc having a diameter of 65 mm or less and a thickness between andincluding 0.4 mm and 0.7 mm, a recording area on the disc extendingoutwardly from a radial position 12.5 mm or less from a center of thedisc, the recording area having a storage capacity of at least 2Gigabytes, a ratio between the recording area and a non-recording areaof the disc being 3.4 or more, the disc cartridge comprising: acartridge having a rectangular shape and including a first side having alength between and including 52 mm and 70 mm, and a second side,perpendicular to the first side, having a length between and including52 mm and 70 mm, the cartridge having a thickness between and including3 mm and 6 mm; at least one opening formed in a side of the cartridgeparallel to the read/write recording medium, the opening being a writingand reading access opening through which a radially extending portion ofthe recording medium is exposed to a light beam from an optical pickupand through which a magnetic-clamping hub is exposed, the openingfurther being formed deviated to one lateral side from a middle point ofa front side of the cartridge; a center hole formed through the centerof the disc; and an annular table-abutment integrally formed as a partof the disc around and adjacent the center hole and being convex to oneside of the disc, the annular table-abutment having a recessed portionhaving a surface that faces away from the one side of the disc andrecessed toward the one side of the disc, the hub being fixed to a thesurface of the recessed portion of the annular table-abutment, the hubhaving a flange portion fixed to the surface of the recessed portion ofthe table-abutment on the surface of the table-abutment that faces awayfrom the one side of the disc and a depressed portion depressed from theflange portion into the center hole toward the one side of the disc, aheight of the hub from a lower surface of the depressed portion to anupper surface of the flange portion being smaller than a thickness ofthe table-abutment.
 2. The disc cartridge according to claim 1, furthercomprising: a shutter member slidably mounted along one lateral side ofthe cartridge for opening and closing at least the writing accessopening and reading access opening formed in the cartridge.
 3. A disccartridge having a read-only optical recording medium encased therein,the read-only optical recording medium including a disc having adiameter of 65 mm or less and a thickness between and including 0.4 mmand 0.7 mm, a recording area on the disc extending outwardly from aradial position 12.5 mm or less from a center of the disc, the recordingarea having a storage capacity of at least 2 Gigabytes, a ratio betweenthe recording area and a non-recording area of the disc being 3.4 ormore, the disc cartridge comprising: a cartridge of a rectangular shapeincluding a first side having a length between and including 52 mm and70 mm and a second side, perpendicular to the first side, having alength between and including 52 mm and 75 mm, the cartridge having athickness between and including 3 mm and 6 mm; at least one openingformed in a side of the cartridge parallel to the read-only recordingmedium, the opening being a writing and reading access opening throughwhich a radially extending portion of the recording medium is exposed toa light beam from an optical pickup through which a magnetic-clampinghub is exposed, the opening further being formed deviated to one lateralside from a middle point of a front side of the cartridge; a center holeformed through the center of the disc; and an annular table-abutmentintegrally formed as a part of the disc around and adjacent the centerhole and being convex to one side of the disc, the annulartable-abutment having a recessed portion having a surface that facesaway from the one side of the disc and is recessed toward the one sideof the disc, the hub being fixed to a the surface of the recessedportion of the annular table-abutment, the hub having a flange portionfixed to the surface of the recessed portion of the table-abutment onthe surface of the table-abutment that faces away from the one side ofthe disc and a depressed portion depressed from the flange portion intothe center hole toward the one side of the disc, a height of the hubfrom a lower surface of the depressed portion to an upper surface of theflange portion being smaller than a thickness of the table-abutment. 4.The disc cartridge according to claim 3, further comprising: a shuttermember slidably mounted along one lateral side of the cartridge foropening and closing at least the writing access opening and readingaccess opening formed in the cartridge.